Find the sum 1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + ... + 301 + 302. (The pattern of signs is + + - - + + - - ...)
Evaluate the terms whenever one + + - - occurs.
For example.
1 + 2 - 3 - 4 = -4
5 + 6 - 7 - 8 = -4
Then find how many + + - - s are there
+26393 Find the sum 1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + ... + 301 + 302.
(The pattern of signs is + + - - + + - - ...)
\(\begin{array}{|rll|} \hline && 1 \\ && \underbrace{+2 - 3}_{-1} \underbrace{ - 4 + 5}_{+1}\\ && \underbrace{ + 6 - 7}_{-1} \underbrace{ - 8 + 9}_{+1} \\ && + \ldots \\ && \underbrace{+298 - 299}_{-1} \underbrace{-300 + 301}_{+1} \\ && + 302 \\ &=& 1+0+302 \\ &=& \mathbf{303} \\ \hline \end{array} \)
